Lipoxins are a group of biologically active mediators derived from arachidonic acid through the action of lipoxygenase (LO) enzyme systems. (Serhan, C. N. and Samuelsson, B. (1984) Proc. Natl. Acad. Sci. USA 81:5335). Formulation in human cell types is initiated by 5-LO or 15-LO. (Serhan, C. N. (1991) J. Bioenerg. Biomembr. 23:105). Single-cell types generate lipoxins at nanogram levels during human neutrophil-platelet and eosinophil transcellular biosynthesis of eicosanoids. (Serhan, C. N. and Sheppard, K.-A. (1990) J. Clin. Invest. 85:772). LXs are conjugated tetraene-containing eicosanoids that modulate cellular events in several organ systems.
Lipoxin A4 (LXA4) and lipoxin B4 (LXB4) are the two major lipoxins. Each enhances protein kinase C (PKC) activity in nuclei of erythroleukemia cells at 10 nM (Beckman, B. S. et al. (1992) Proc. Soc. Exp. Biol. Med. 201:169). Each elicits prompt vasodilation at nM levels (Busija, D. W. et al. (1989) Am. J. Physiol. 256:H468; Katoh, T. et al. (1992) Am. J. Physiol. 263 (Renal Fluid Electrolyte Physiol. 32):F436). The vasodilatory effects of lipoxins are well-documented. For example, administration of LXA4 in micromolar amounts via inhalation blocks bronchoconstriction in asthmatic patients. (Christie, P. E. et al. (1992) Am. Rev. Respir. Dis. 145:1281).
In the 10−10 M range, LXA4 also stimulates cell proliferation in combination with suboptimal concentrations of granulocyte-macrophage colony stimulating factor (GM-CSF) to induce myeloid bone marrow colony formation (Stenke, L. et al. (1991) Biochem. Biophys. Res. Commun. 180:255). LXA4 also stimulates human mononuclear cell colony formation (Popov, G. K. et al. (1989) Bull. Exp. Biol. Med. 107:93).
LXA4 inhibits chemotaxis of polymorphonuclear leukocytes (Lee, T. H. et al. (1991) Biochem. Biophys. Res. Commun. 180:1416). An equimolar combination of lipoxins has been found to modulate the polymorphonuclear neutrophil-mesangial cell interaction in glomerular inflammation (Brady, H. R. et al (1990) Am. J. Physiol. 809). Activation of the polymorphonuclear neutrophils (PMN) includes the release of mediators of structural and functional abnormalities associated with the early stages of glomerular inflammation. (Wilson, C. B. and Dixon, F. J. (1986) In: The Kidney, edited by B. M. Brenner and F. C. Rector. Philadelphia, Pa.: Saunders, p. 800-891).
Lipoxins act as antagonists to leukotrienes (LT), which are mediators of inflammation. LXA4 modulates LTC4-induced obstruction of airways in asthmatic patients. (Christie, P. E. et al. (1992) Am. Rev. Respir. Dis. 145:1281). LXA4 inhibits LTD4- and LTB4-mediated inflammation in animal in vivo models. (Badr, K. F. et al. (1989) Proc. Natl. Acad. Sci. 86:3438; Hedqvist, P. et al. (1989) Acta Physiol. Scand. 137:571). Prior exposure to LXA4 (nM) blocks renal vasoconstrictor actions of LTD4 (Katoh, T. et al (1992) Am. J. Physiol. 263 (Renal Fluid Electrolyte Physiol. 32) F436). Leukotriene-induced inflammation occurs, for example, in arthritis, asthma, various types of shock, hypertension, renal diseases, allergic reactions, and circulatory diseases including myocardial infarction.
Although lipoxins are potent small molecules that could be administered in vivo to treat a number of diseases and conditions, these molecules are short-lived in vivo. Compounds having the same bio-activities as natural lipoxins, but a longer in vivo half-life would be valuable pharmaceuticals.